Oil pump for internal combustion engine

ABSTRACT

A first fitting portion is coupled to a protruding end of the crankshaft to be rotatable about a crankshaft rotational axis. An intermediate member includes a first hole wall slidably supporting the first fitting portion in a first direction orthogonal to the crankshaft rotational axis so that the intermediate member rotates together with the crankshaft. An inner rotor includes a second hole wall slidably supporting the second fitting portion in a second direction orthogonal to the first direction and the crankshaft rotational axis so that the inner rotor rotates together with the intermediate member. One of the first direction and the second direction is in parallel with a line segment joining the crankshaft rotational axis and an axis of a crankpin of the internal combustion engine which is closest to the protruding end of the crankshaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U. S. C. §119 to Japanese Patent Application No. 2015-139434, filed Jul. 13, 2015. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an oil pump for an internal combustion engine.

Discussion of the Background

For example, Japanese Patent Application Publication No. H08-135422 describes an internal combustion engine which has a trochoid oil pump provided coaxially at one end of a crankshaft. The oil pump of this type has an inner rotor coaxially and directly coupled to the crankshaft, and therefore a power transmission mechanism such as a chain mechanism can be omitted, which is advantageous in terms of size reduction and friction reduction of the internal combustion engine. In addition, the inner rotor is provided with a cylindrical boss portion on one end face thereof and this boss portion is fitted in a socket-and-spigot fashion to a hole of a pump housing, thereby suppressing oil leakage through the gap between the inner rotor and the pump housing and suppressing a reduction in pump efficiency.

For example, PCT International Application No. 2002-540368 discloses a coupling structure between the drive shaft and a gear of a fuel pump in which the drive shaft and the gear are connected to each other via a coupling member that tolerates misalignment. In the coupling structure disclosed in PCT International Application No. 2002-540368, the tip of the drive shaft is formed in a flat shape, and is fitted in a long hole formed in the coupling member so that the drive shaft is capable of displacement and rotates together with the coupling member. The coupling member is fitted in a notch formed in a central part of the gear with a clearance (play) in between. Since the drive shaft is capable of displacement with respect to the long hole and the coupling member is capable of displacement with respect to the notch, the misalignment between the drive shaft and the gear is tolerated.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an oil pump for an internal combustion engine has: a crankshaft that is supported on an internal combustion engine body so as to be rotatable about a predetermined crank axis; an inner rotor that is connected to one end of the crankshaft via an Oldham's coupling; and an outer rotor that is rotatably accommodated in a pump housing coupled to the internal combustion engine body, and meshes at an inner circumferential part thereof with an outer circumferential part of the inner rotor, the oil pump being characterized in that the Oldham's coupling has: a first fitting portion that is provided at the one end of the crankshaft; an intermediate member that includes a first fitting hole accommodating the first fitting portion so that the first fitting portion is slidable in a first direction orthogonal to an axis of the crankshaft and rotates together with the first fitting hole, and a second fitting portion; and a second fitting hole that accommodates the second fitting portion so that the second fitting portion is slidable in a second direction orthogonal to the first direction and rotates together with the second fitting hole, and the first direction or the second direction extends parallel with a line segment that joins an axis of a crankpin closest to the one end of the crankshaft and the axis of the crankshaft.

According to another aspect of the present invention, an oil pump for an internal combustion engine includes a pump housing, a crankshaft, a first fitting portion, an intermediate member, an inner rotor, and an outer rotor. The pump housing is coupled to an engine body of the internal combustion engine. The crankshaft is supported on the engine body to be rotatable about a crankshaft rotational axis. The crankshaft has a protruding end protruding from the engine body. The first fitting portion is coupled to the protruding end of the crankshaft. The intermediate member is slidably coupled to the first fitting portion. The intermediate member includes a first hole wall and a second fitting portion. The first hole wall surrounds the crankshaft rotational axis and defines a first fitting hole in which the first fitting portion is provided. The first hole wall slidably supports the first fitting portion in a first direction orthogonal to the crankshaft rotational axis so that the intermediate member rotates together with the crankshaft. The second fitting portion is provided to be opposite to and around the first hole wall. The inner rotor is slidably coupled to the intermediate member to be rotatable about an inner rotor rotational axis parallel to the crankshaft rotational axis. The inner rotor includes a second hole wall and an inner rotor outer circumferential part. The second hole wall surrounds the inner rotor rotational axis and defines a second fitting hole in which the second fitting portion is provided. The second hole wall slidably supports the second fitting portion in a second direction orthogonal to the first direction and the crankshaft rotational axis so that the inner rotor rotates together with the intermediate member. One of the first direction and the second direction is in parallel with a line segment joining the crankshaft rotational axis and an axis of a crankpin of the internal combustion engine which is closest to the protruding end of the crankshaft. The inner rotor outer circumferential part is provided to be opposite to and around the second hole wall. The outer rotor is accommodated in the pump housing to be rotatable about an outer rotor rotational axis parallel to the crankshaft rotational axis and includes an outer rotor inner circumferential part surrounding the outer rotor rotational axis to mesh with the inner rotor outer circumferential part.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

FIG. 1 is a sectional view of an oil pump of an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a sectional view illustrating an enlarged main part of the oil pump.

FIG. 3 is a sectional view illustrating the direction of an Oldham's coupling with respect to a crankshaft.

FIG. 4 is a sectional view illustrating the direction of an Oldham's coupling with respect to a crankshaft according to a modified example.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

Hereinbelow, a description is given of an embodiment where the present invention is applied to an internal combustion engine of an automobile.

As illustrated in FIG. 1, an oil pump 1 is mounted to an internal combustion engine body 2 (an engine body 2 of an internal combustion engine). The internal combustion engine body 2 includes: a cylinder block 3; a cylinder head that is coupled to an upper part of the cylinder block 3; an oil pan that is coupled to a lower part of the cylinder block 3; a head cover that is coupled to an upper part of the cylinder head; a chain cover 4 that is coupled to side parts of the cylinder block 3 and the cylinder head; and the like. The cylinder block 3 has: an upper part that has at least one cylinder; and a lower part that communicates with the lower end of each cylinder, opens toward the bottom, and has a crank chamber inside. In the crank chamber, a crankshaft 5 is rotatably disposed in parallel with the cylinder array direction. The lower part of the cylinder block 3 has end walls 3A on both ends of the crankshaft 5 in the direction along the axis thereof (hereinafter referred to as a crankshaft rotational axis A or an axis A), and has one or more bearing walls between both end walls 3A so that they partition the crank chamber according to the number of cylinders. The crankshaft 5 is rotatably supported by the end walls 3A and the bearing walls.

The chain cover 4 is a platy member extending vertically, and is disposed to cover end faces of the cylinder block 3 and the cylinder head on one side thereof in the direction of the axis A. The chain cover 4 has both side edges coupled to the cylinder block 3 and the cylinder head, and defines a vertically extending chain chamber 7 between itself and the end faces of the cylinder block 3 and the cylinder head. The upper end of the chain cover 4 is coupled to the head cover extending to one side from the cylinder head, and the chain chamber 7 communicates with a valve chamber formed between the head cover and the cylinder head. The lower end of the chain cover 4 is coupled to the oil pan extending to one side from the cylinder block 3, and the chain chamber 7 communicates with a space inside the oil pan.

The crankshaft 5 has a protruding end 5A that protrudes to the inside of the chain chamber 7 from the end wall 3A disposed on one end side of the cylinder block 3. In the direction of the axis A, the protruding end 5A side is referred to as a distal side and the cylinder block side is referred to as a proximal side. The oil pump 1 is provided in the chain cover 4 at a portion corresponding to the protruding end 5A of the crankshaft 5. The protruding end 5A of the crankshaft 5 penetrates the oil pump 1 and extends toward an outer face of the chain cover 4. The protruding end 5A of the crankshaft 5 has a circular cross section, and is disposed coaxially with a crank journal 5B rotatably supported by the end walls 3A. The protruding end 5A of the crankshaft 5 has an outer diameter formed smaller than that of the crank journal 5B, and forms a shoulder face 5C at the boundary between itself and the crank journal 5B.

On an outer circumferential part of the protruding end 5A, a sprocket 11 and a crank pulley 12 are mounted in this order from the proximal side (crank journal 5B side). The sprocket 11 has: a cylindrical base 11A that opens at both ends thereof; sprocket teeth 11B that are formed on an outer circumferential face of the base 11A; and a flange 11C that is formed on one end of the cylindrical part of the sprocket. The sprocket 11 is mounted on the protruding end 5A so that the protruding end 5A is inserted inside the cylindrical part and the flange 11C comes in contact with the shoulder face 5C. The base 11A is coupled to the outer circumferential part of the protruding end 5A via a key and thus rotates integrally with the protruding end 5A.

The crank pulley 12 has: a circular pulley body portion 12A; and a cylinder-shaped pulley cylindrical portion 12B that is provided at the center of the pulley body portion 12A coaxially with the pulley body portion. A distal side portion of the protruding end 5A is inserted inside the pulley cylindrical portion 12B. The axial position of the crank pulley 12 with respect to the crankshaft 5 is fixed by the contact of a tip face of the pulley cylindrical portion 12B with an end face of the base 11A of the sprocket 11. In addition, the pulley cylindrical portion 12B is coupled to the outer circumferential part of the protruding end 5A via a key 15 and thus rotates integrally with the protruding end 5A. A fastening plate 16 to pinch the cylindrical part of the sprocket 11 and the pulley cylindrical portion 12B between itself and the shoulder face 5C is coupled to the tip of the protruding end 5A with a bolt 17. In the state where the crank pulley 12 is coupled to the protruding end 5A, the pulley cylindrical portion 12B is partially placed inside the oil pump 1 and the pulley body portion 12A is placed outside the oil pump 1 (chain cover 4).

An endless timing chain 18 is wound around the sprocket teeth 11B of the sprocket 11, and the timing chain 18 is used to connect the sprocket 11 to sprockets of intake and exhaust camshafts provided in the cylinder head. An endless accessory driving belt 19 is wound around an outer circumferential part of the pulley body portion 12A of the crank pulley 12, and the accessory driving belt 19 is used to connect the crank pulley 12 to pulleys of drive shafts of engine accessories such as an ACG and an air conditioning compressor.

As illustrated in FIGS. 1 to 3, the oil pump 1 is a trochoid pump, and has: a pump housing 21; an outer rotor 22; an inner rotor 23; and an Oldham's coupling 24 that connects the inner rotor 23 and the pulley cylindrical portion 12B. The pump housing 21 has: a housing body portion 31 that is formed integrally in the chain cover 4; and a housing lid portion 33 that is fastened to the housing body portion 31 with a bolt 32.

As illustrated in FIGS. 1 and 2, the housing body portion 31 has: a substantially cylindrical circumferential wall portion 31A that has, as its center, an axis B parallel with the axis A; and a distal-side wall portion 31B that is provided to close a distal-side end part of the circumferential wall portion 31A in the direction of the axis A. An outer circumferential part of the circumferential wall portion 31A is coupled to the chain cover 4. In the distal-side wall portion 31B, a body-side insertion hole 34 having the axis A as its center and penetrating in the direction of the axis A is formed. The body-side insertion hole 34 has a circular cross section, and its inner diameter is formed larger than the outer diameter of the pulley cylindrical portion 12B.

The housing lid portion 33 has a proximal-side wall portion 33A that is disposed to close a proximal-side end part of the circumferential wall portion 31A in the direction of the axis A. The proximal-side wall portion 33A is opposed to the distal-side wall portion 31B with a distance in between. In the proximal-side wall portion 33A, a lid-side insertion hole 35 having the axis A as its center and penetrating in the direction of the axis A is formed. The lid-side insertion hole 35 has a circular cross section, and its inner diameter is formed larger than the outer diameter of the pulley cylindrical portion 12B and smaller than the inner diameter of the body-side insertion hole 34.

The housing lid portion 33 is coupled to the housing body portion 31, and thereby a cylindrical rotor holder 36 surrounded by the distal-side wall portion 31B, the circumferential wall portion 31A, and the proximal-side wall portion 33A is formed. The rotor holder 36 is a cylindrical space having, as its center, the axis B being offset parallel to the axis A. The rotor holder 36 houses the inner rotor 23 and the outer rotor 22.

In the distal-side wall portion 31B and the proximal-side wall portion 33A, an oil inlet passage 38 and an oil discharge passage 39 communicating with the rotor holder 36 are formed.

The outer rotor 22 is a ring-shaped internal gear, and has: an outer circumferential face that is formed on its circumferential face; and trochoid curve-shaped internal teeth that are formed in its inner circumferential part (an outer rotor inner circumferential part). Both end faces of the outer rotor 22 in its axial direction are formed on a plane orthogonal to its axis. The outer rotor 22 is rotatably fitted to the rotor holder 36. Thereby, the outer rotor 22 rotates about the axis B (i.e. the axis B is an outer rotor rotational axis B) while its outer circumferential face is in sliding contact with the inner circumferential face of the circumferential wall portion 31A. Both end faces of the outer rotor 22 are in sliding contact with the distal-side wall portion 31B and the proximal-side wall portion 33A, which restricts the movement of the outer rotor in the direction of the axis B.

The inner rotor 23 is an external gear, and has trochoid curve-shaped external teeth in its outer circumferential part (an inner rotor outer circumferential part). Both end faces of the inner rotor 23 in its axial direction are formed on a plane orthogonal to its axis. The inner rotor 23 is housed in the rotor holder 36 at a position inside the outer rotor 22, and its both end faces are in sliding contact with the distal-side wall portion 31B and the proximal-side wall portion 33A. A cylindrical boss portion 23A protruding axially is formed on the end face of the inner rotor 23 that is in sliding contact with the distal-side wall portion 31B. The boss portion 23A is rotatably fitted in the body-side insertion hole 34 of the distal-side wall portion 31B. Since the boss portion 23A is fitted in a socket-and-spigot fashion to the body-side insertion hole 34, the rotation center of the inner rotor 23 with respect to the housing body portion 31 is fixed and thus the inner rotor rotates about the axis A. Both end faces of the inner rotor 23 are in sliding contact with the distal-side wall portion 31B and the proximal-side wall portion 33A, which restricts the movement of the inner rotor in the direction of the axis A.

The pulley cylindrical portion 12B and the inner rotor 23 are connected to each other via the Oldham's coupling 24. As illustrated in FIGS. 2 and 3, the Oldham's coupling 24 has: a first fitting portion 41 that is provided in the pulley cylindrical portion 12B; an intermediate member 40 that includes a first fitting hole 42, accommodating the first fitting portion 41, and a second fitting portion 43; and a second fitting hole 44 that is formed in the inner rotor 23 and accommodates the second fitting portion 43.

As illustrated in FIGS. 1 and 2, a proximal-side portion (sprocket 11-side portion) of an outer circumferential face of the pulley cylindrical portion 12B has a diameter by far smaller than a distal-side portion (pulley body portion 12A-side portion) thereof. At the boundary between the proximal-side portion and the distal-side portion, a restriction wall 12C that is directed to the proximal side and constitutes a face orthogonal to the axis of the pulley cylindrical portion 12B is formed. As illustrated in FIGS. 1 to 3, the first fitting portion 41 is formed on the proximal-side portion of the outer circumferential face of the pulley cylindrical portion 12B. The first fitting portion 41 has: a pair of first side faces 41A that are arranged with the axis A interposed therebetween; and a pair of arcuate first side end faces 41B that join opposed end parts of the pair of first side faces 41A. In a transverse section of the pulley cylindrical portion 12B, the paired first side faces 41A are formed in opposed planes parallel with each other and each extend in a first direction. The paired first side end faces 41B are each formed in the shape of an arcuate circumferential face having the axis A as its center.

The first fitting hole 42 is formed in a central part of the intermediate member 40, and the second fitting portion 43 is formed in an outer circumferential part of the intermediate member 40. The first fitting hole 42 is a through hole, and has: a pair of first hole wall faces 42A composed of opposed flat faces parallel with each other; and a pair of arcuate first hole wall end faces 42B that join opposed end parts of the pair of first hole wall faces 42A. The pair of first hole wall faces 42A and the pair of arcuate first hole wall end faces 42B can be referred to as a first hole wall. The first fitting portion 41 is inserted in the first fitting hole 42, whereby the intermediate member 40 is supported on the outer circumference of the pulley cylindrical portion 12B. The paired first hole wall faces 42A are formed to be in sliding contact with the respective first side faces 41A and extend in the first direction. Each first hole wall face 42A is formed longer than the corresponding first side face 41A in the first direction. Thereby, the intermediate member 40 and the pulley cylindrical portion 12B are movable relative to each other in the first direction. Since the first hole wall faces 42A are in sliding contact with the corresponding first side faces 41A, the intermediate member 40 is rotated together with the pulley cylindrical portion 12B at the same number of revolutions.

Each first hole wall end face 42B is formed to have a curvature smaller than the curvature of each first side end face 41B. Thereby, even when the first fitting portion 41 moves in the first direction inside the first fitting hole 42 and the first side end face 41B comes closest to the first hole wall end face 42B, a clearance is formed between the first side end face 41B and the first hole wall end face 42B.

The second fitting portion 43 has: a pair of second side faces 43A that are arranged with the first fitting hole 42 interposed therebetween; and a pair of arcuate second side end faces 43B that join opposed end parts of the pair of second side faces 43A. In a transverse section of the pulley cylindrical portion 12B, the paired second side faces 43A are formed in opposed planes parallel with each other and each extend in a second direction orthogonal to the first direction.

In the direction of the axis A, the distal-side end face and proximal-side end face of the intermediate member 40 are formed in planes orthogonal to the axis A. The position of the intermediate member 40 in the direction of the axis A with respect to the crankshaft 5 and the oil pump 1 is fixed by the sliding contact of the distal-side end face of the intermediate member 40 with the restriction wall 12C and the sliding contact of the proximal-side end face thereof with the proximal-side wall portion 33A.

The second fitting hole 44 is a through hole formed in a central part of the inner rotor 23 and open at both end faces of the inner rotor 23. The second fitting hole 44 has: a pair of second hole wall faces 44A composed of opposed flat faces parallel with each other; and a pair of arcuate second hole wall end faces 44B that join opposed end parts of the pair of second hole wall faces 44A. The pair of second hole wall faces 44A and the pair of arcuate second hole wall end faces 44B can be referred to as a second hole wall. The second fitting portion 43 is inserted in the second fitting hole 44, whereby the inner rotor 23 is supported on the outer circumference of the intermediate member 40. The paired second hole wall faces 44A are formed to be in sliding contact with the second side faces 43A and extend in the second direction. Each second hole wall face 44A is formed longer than the corresponding second side face 43A in the second direction. Thereby, the inner rotor 23 and the intermediate member 40 are movable relative to each other in the second direction. Since the second hole wall faces 44A are in sliding contact with the corresponding second side faces 43A, the inner rotor 23 is rotated in response to the driving of the pulley cylindrical portion 12B via the Oldham's coupling 24 at the same angular velocity.

Each second hole wall end face 44B is formed to have a curvature smaller than the curvature of each second side end face 43B. Thereby, even when the second fitting portion 43 moves in the second direction inside the second fitting hole 44 and the second side end face 43B comes closest to the second hole wall end face 44B, there is a clearance formed between the second side end face 43B and the second hole wall end face 44B.

The first fitting portion 41, the first fitting hole 42, the second fitting portion 43, and the second fitting hole 44 are arranged on one plane orthogonal to the axis A.

An annular oil seal 60 is mounted in the space between a hole wall face of the body-side insertion hole 34 and the outer circumferential face of the pulley cylindrical portion 12B. The oil seal 60 is designed to seal the space between the hole wall face of the body-side insertion hole 34 and the outer circumferential face of the pulley cylindrical portion 12B to block the passage of oil. Various forms of known oil seal can be employed as the oil seal 60.

Correspondingly to each cylinder, the crankshaft 5 has a crankpin 50 that is offset parallel to the axis A. Each crankpin 50 spans the space between a pair of crank webs 51 that extend radially from the crank journal 5B. As illustrated in FIG. 2, reference numeral C represents a line segment that joins an axis 50A of the crankpin 50 closest to the protruding end 5A and the axis A of the crankshaft 5 as seen in the direction along the axis A. In this embodiment, the first direction (i.e., the first side faces 41A and the first hole wall faces 42A) is placed parallel to the line segment C, whereas the second direction (i.e., the second side faces 43A and the second hole wall faces 44A) is placed perpendicular to the line segment C.

A description is given of the workings and effect of the oil pump 1 having the above configuration. The pulley cylindrical portion 12B (crankshaft 5) and the inner rotor 23 are connected to each other via the Oldham's coupling 24. Accordingly, in the case where there is misalignment between the axis center of the pulley cylindrical portion 12B (crankshaft 5) and the axis center of the inner rotor 23 (pump housing 21), the first fitting portion 41 is displaced in the first direction with respect to the first fitting hole 42 and the second fitting portion 43 is displaced in the second direction with respect to the second fitting hole 44, whereby the misalignment between the axis center of the pulley cylindrical portion 12B and the axis center of the inner rotor 23 is tolerated. This enables the inner rotor 23 to rotate with respect to the pump housing 21 about a predetermined rotation axis smoothly at the same angular velocity as the pulley cylindrical portion 12B.

In addition, the first direction in which the first fitting portion 41 slides with respect to the first fitting hole 42 extends parallel with the line segment C that joins the axis 50A of the crankpin 50 closest to the protruding end 5A of the crankshaft 5 and the axis A of the crankshaft 5. Accordingly, the deformation of the crankshaft 5 caused by combustion of the cylinder closest to the protruding end 5A is relieved smoothly, and thus becomes less likely to affect the inner rotor 23. The protruding end 5A of the crankshaft 5 is likely to be deformed in a specific radial direction upon receiving a load caused by the cylinder closest to the protruding end 5A at an early stage of the expansion stroke. This load at the early stage of the expansion stroke is applied as a load to push the crankpin 50 of the cylinder, closest to the protruding end 5A, in the cylinder axis direction. In other words, this crankpin 50 is pushed downward along the line segment C that joins the axis 50A of the crankpin 50 closest to the protruding end 5A of the crankshaft 5 and the axis A of the crankshaft 5. Because the crankshaft 5 is supported on the end walls 3A, the protruding end 5A is displaced upward in the direction along the line segment C once the crankpin 50 close to the protruding end 5A is pushed downward along the line segment C. Since the first direction is placed parallel to the line segment C, the displacement of the protruding end 5A due to the load applied on the crankshaft 5 at the early stage of the expansion stroke is absorbed smoothly by the first fitting portion 41 and the first fitting hole 42.

Since the first fitting portion 41, the first fitting hole 42, the second fitting portion 43, and the second fitting hole 44 are arranged on one plane orthogonal to the axis A of the crankshaft 5, the axial length of the Oldham's coupling 24 is small. Moreover, in the radial direction of the crankshaft 5, the Oldham's coupling 24 is disposed between the crankshaft 5 and the inner rotor 23. These enable a reduction of the length of the internal combustion engine body 2 in the direction of the axis of the crankshaft 5.

Since the curvature of each first hole wall end face 42B is smaller than the curvature of each first side end face 41B, a clearance is formed between the first side end face 41B and the first hole wall end face 42B even when the first side end face 41B and the first hole wall end face 42B come closest to each other. Accordingly, a space is formed between each first side end face 41B and the corresponding first hole wall end face 42B irrespective of the position of the first fitting portion 41 with respect to the first fitting hole 42, and oil (lubricating oil) is held in this space. Likewise, since the curvature of each second hole wall end face 44B is smaller than the curvature of each second side end face 43B, a clearance is formed between the second side end face 43B and the second hole wall end face 44B even when the second side end face 43B and the second hole wall end face 44B come closest to each other. Accordingly, a space is formed between each second side end face 43B and the corresponding second hole wall end face 44B irrespective of the position of the second fitting portion 43 with respect to the second fitting hole 44, and oil is held in this space. By filling the first fitting hole 42 and the second fitting hole 44 with oil, this oil cushions the sliding movement of the first fitting portion 41 and the second fitting portion 43.

Since the oil seal 60 is provided between the body-side insertion hole 34 of the pump housing 21 and the pulley cylindrical portion, oil having leaked out toward the pulley cylindrical portion 12B through the sliding contact faces of the inner rotor 23 and the distal-side wall portion 31B is blocked from flowing toward the pulley body portion 12A. In addition, since the clearance extending between the first fitting portion 41 and the first fitting hole 42 along the axis A and the clearance extending between the second fitting portion 43 and the second fitting hole 44 along the axis A are formed between the inner rotor 23 and the pulley cylindrical portion 12B, oil having leaked out through the sliding contact faces of the inner rotor 23 and the distal-side wall portion 31B can flow into the lid-side insertion hole 35 through these clearances and is discharged into the chain chamber 7 through the lid-side insertion hole 35. Besides, a groove extending in the axis direction may be provided in each first side face 41A of the intermediate member 40 to facilitate the flow of oil from the body-side insertion hole 34 to the lid-side insertion hole 35. In another embodiment, the distal-side wall portion 31B may be provided with a discharge passage that communicates with the body-side insertion hole 34 and a portion of the outer circumferential part of the circumferential wall portion 31A corresponding to an inner face side of the chain cover 4. These inhibit excess hydraulic pressure of oil from being applied on the oil seal 60, and thereby prevent leakage of oil and breakage of the oil seal 60. Oil having leaked out toward the pulley cylindrical portion 12B through the sliding contact faces of the inner rotor 23 and the proximal-side wall portion 33A is discharged into the chain chamber 7 through the lid-side insertion hole 35. The oil discharged into the chain chamber 7 is collected by the oil pan.

While this is the end of the description of the specific embodiments, the present invention is not limited to the above embodiments but can be embodied in various ways. Although in the above embodiments the first direction (the first side faces 41A and the first hole wall faces 42A) is placed parallel to the line segment C, the second direction (the second side faces 43A and the second hole wall faces 44A) may be placed parallel to the line segment C instead as illustrated in FIG. 4.

In the above embodiments, the first fitting portion 41 is formed in the pulley cylindrical portion 12B coupled integrally to the crankshaft 5. However, it is also possible to omit or shorten the pulley cylindrical portion 12B and form the first fitting portion 41 directly in the outer circumferential part of the protruding end 5A of the crankshaft 5. In addition, the housing body portion 31 of the pump housing 21 does not necessarily have to be formed in the chain cover 4 but may be formed in the end walls of the cylinder block 3 or other members coupled to the cylinder block 3.

According to one mode of the present invention, an oil pump (1) for an internal combustion engine has: a crankshaft (5) that is supported on an internal combustion engine body (2) so as to be rotatable about a predetermined crank axis (A); an inner rotor (23) that is connected to one end of the crankshaft via an Oldham's coupling (24); and an outer rotor (22) that is rotatably accommodated in a pump housing (21) coupled to the internal combustion engine body, and meshes at an inner circumferential part thereof with an outer circumferential part of the inner rotor, the oil pump being characterized in that the Oldham's coupling has: a first fitting portion (41) that is provided at the one end of the crankshaft; an intermediate member (40) that includes a first fitting hole (42) accommodating the first fitting portion so that the first fitting portion is slidable in a first direction orthogonal to an axis of the crankshaft and rotates together with the first fitting hole, and a second fitting portion (43); and a second fitting hole (44) that accommodates the second fitting portion so that the second fitting portion is slidable in a second direction orthogonal to the first direction and rotates together with the second fitting hole, and the first direction or the second direction extends parallel with a line segment (C) that joins an axis (50A) of a crankpin (50) closest to the one end of the crankshaft and the axis of the crankshaft.

According to this mode, since the crankshaft and the inner rotor are connected to each other via the Oldham's coupling, misalignment between the axis center of the crankshaft and that of the pump housing is tolerated, thus enabling the inner rotor to rotate with respect to the pump housing about a predetermined rotation axis smoothly at the same angular velocity as the crankshaft. The one end of the crankshaft is likely to be deformed in a specific radial direction upon receiving a load caused by a cylinder closest to the one end during the expansion stroke. Because this load during the expansion stroke becomes the largest when the piston of the cylinder closest to the one end comes near a position 15 degrees after the compression top dead center position, the one end of the crankshaft is likely to be deformed in a direction substantially parallel with the line segment that joins the axis of the crankpin closest to the one end of the crankshaft and the axis of the crankshaft. Since the first direction, in which the crankshaft slides with respect to the intermediate member, or the second direction, in which the inner rotor slides with respect to the intermediate member, extends parallel with the line segment that joins the axis of the crankpin closest to the one end of the crankshaft and the axis of the crankshaft, the displacement of the crankshaft is relieved smoothly, and thus becomes less likely to affect the inner rotor.

Further, in the above mode, it is preferable that the first fitting portion, the first fitting hole, the second fitting portion, and the second fitting hole are arranged on one plane orthogonal to the axis of the crankshaft.

According to this mode, the axial length of the Oldham's coupling 24 can be made small. Moreover, in the radial direction of the crankshaft, the Oldham's coupling can be disposed between the crankshaft and the inner rotor. These enable a reduction of the length of the internal combustion engine in the direction of the axis of the crankshaft.

Further, in the above mode, it is preferable that the first fitting portion has: a pair of first side faces (41A) that extend parallel with the first direction with the axis of the crankshaft interposed therebetween; and a pair of arcuate first side end faces (41B) that join opposed end parts of the pair of first side faces, the first fitting hole has: a pair of planar first hole wall faces (42A) that are in sliding contact with the paired first side faces respectively; and a pair of arcuate first hole wall end faces (42B) that join opposed end parts of the pair of first hole wall faces, and each first hole wall end face has a curvature smaller than each first side end face.

According to this mode, since the paired first side faces are in sliding contact with the paired first hole wall faces respectively, the first fitting portion is fitted in the first fitting hole so as to be slidable in the first direction and rotate together with the first fitting hole. In addition, a space is formed between each first side end face and the corresponding first hole wall end face irrespective of the position of the first fitting portion with respect to the first fitting hole, and thus oil (lubricating oil) can be held in this space.

Further, in the above mode, it is preferable that the second fitting portion has: a pair of second side faces (43A) that extend parallel with the second direction with the axis of the crankshaft interposed therebetween; and a pair of arcuate second side end faces (43B) that join opposed end parts of the pair of second side faces, the second fitting hole has: a pair of planar second hole wall faces (44A) that are in sliding contact with the paired second side faces respectively; and a pair of arcuate second hole wall end faces (44B) that join opposed end parts of the pair of second hole wall faces, and each second hole wall end face has a curvature smaller than each second side end face.

According to this mode, since the paired second side faces are in sliding contact with the paired second hole wall faces respectively, the second fitting portion is fitted in the second fitting hole so as to be slidable in the second direction and rotate together with the second fitting hole. In addition, a space is formed between each second side end face and the corresponding second hole wall end face irrespective of the position of the second fitting portion with respect to the second fitting hole, and thus oil (lubricating oil) can be held in this space.

Further, in the above mode, it is preferable that the one end of the crankshaft penetrates the pump housing, the pump housing has, on a distal side thereof in a direction of the axis of the crankshaft, a distal-side wall portion (41B) that is in sliding contact with an end face of the inner rotor on the distal side and has, on a proximal side thereof in the direction of the axis of the crankshaft, a proximal-side wall portion (33A) that is in sliding contact with end faces of the inter rotor and the intermediate member on the proximal side, the crankshaft is provided with a restriction wall (12C) that is in sliding contact with an end face of the intermediate member on the distal side, an oil seal (60) designed to seal a space between the distal-side wall portion and the crankshaft or a member coupled integrally to the crankshaft is provided, the first fitting hole penetrates the intermediate member in the direction of the axis of the crankshaft, and the second fitting hole penetrates the inner rotor in the direction of the axis of the crankshaft.

According to this mode, since the oil seal is provided between the distal-side wall portion and the crankshaft, oil having leaked out through the sliding contact portions of the distal-side wall portion and the distal-side end face of the inner rotor flows to the proximal side of the pump housing through the first fitting hole and the second fitting hole. Thereby, the first fitting hole and the second fitting hole are filled with oil, and serve as a dash pot to cushion the sliding movement of the first fitting portion and the second fitting portion, and also serve as a passage to release oil located on the distal side of the pump housing to the proximal side. Besides, the proximal side of the oil pump preferably communicates with the inside of the internal combustion engine.

Further, in the above mode, it is preferable that the oil pump further has a crank pulley (12) that includes: a circular pulley body portion (12A); and a pulley cylindrical portion (12B) which is provided at the center of the pulley body portion and in which the one end of the crankshaft is inserted unrotatably, the oil pump being characterized in that the first fitting portion is formed in an outer circumferential face of the pulley cylindrical portion.

According to this mode, since the first fitting portion is formed in the pulley cylindrical portion, the length of the crankshaft is short as compared with the case where the pulley cylindrical portion and the first fitting portion are arranged individually.

Further, in the above mode, it is preferable that the internal combustion engine body has: a cylinder block (3); and a chain cover (4) that is coupled to an end wall (3A) of the cylinder block on one end side thereof in the direction of the axis of the crankshaft, and forms a space with the cylinder block therebetween, and the pump housing is provided in the chain cover.

According to this mode, the oil pump and the chain cover can be sub-assembled together. In addition, the rigidity of the membrane surface of the chain cover is increased by the pump housing, and thereby the membrane-surface radiation noise can be reduced.

Further, in the above mode, it is preferable that the inner rotor has a cylindrical boss portion (23A) having an axis of the inner rotor as the center thereof, and the pump housing has a circular fitting hole (34) in which the boss portion is fitted rotatably.

According to this mode, the rotation center of the inner rotor with respect to the pump housing is fixed.

According to the aforementioned modes, it is possible to reduce influence of misalignment between the axis center of an oil pump of an internal combustion engine and that of a crankshaft and their rotational movement relative to each other on the rotational behavior of an inner rotor.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

What is claimed is:
 1. An oil pump for an internal combustion engine, comprising: a crankshaft that is supported on an internal combustion engine body so as to be rotatable about a predetermined crank axis; an inner rotor that is connected to one end of the crankshaft via an Oldham's coupling; and an outer rotor that is rotatably accommodated in a pump housing coupled to the internal combustion engine body, and meshes at an inner circumferential part thereof with an outer circumferential part of the inner rotor, wherein the Oldham's coupling has: a first fitting portion that is provided at the one end of the crankshaft; an intermediate member that includes a first fitting hole accommodating the first fitting portion so that the first fitting portion is slidable in a first direction orthogonal to an axis of the crankshaft and rotates together with the first fitting hole, and a second fitting portion; and a second fitting hole that accommodates the second fitting portion so that the second fitting portion is slidable in a second direction orthogonal to the first direction and rotates together with the second fitting hole, and any one of the first direction and the second direction extends parallel with a line segment that joins an axis of a crankpin closest to the one end of the crankshaft and the axis of the crankshaft.
 2. The oil pump according to claim 1, wherein the first fitting portion, the first fitting hole, the second fitting portion, and the second fitting hole are arranged on one plane orthogonal to the axis of the crankshaft.
 3. The oil pump according to claim 1, wherein the first fitting portion has: a pair of first side faces that extend parallel with the first direction with the axis of the crankshaft interposed therebetween; and a pair of arcuate first side end faces that join opposed end parts of the pair of first side faces, the first fitting hole has: a pair of planar first hole wall faces that are in sliding contact with the paired first side faces respectively; and a pair of arcuate first hole wall end faces that join opposed end parts of the pair of first hole wall faces, and each first hole wall end face has a curvature smaller than each first side end face.
 4. The oil pump according to claim 1, wherein the second fitting portion has: a pair of second side faces that extend parallel with the second direction with the axis of the crankshaft interposed therebetween; and a pair of arcuate second side end faces that join opposed end parts of the pair of second side faces, the second fitting hole has: a pair of planar second hole wall faces that are in sliding contact with the paired second side faces respectively; and a pair of arcuate second hole wall end faces that join opposed end parts of the pair of second hole wall faces, and each second hole wall end face has a curvature smaller than each second side end face.
 5. The oil pump according to claim 1, wherein the one end of the crankshaft penetrates the pump housing, the pump housing has, on a distal side thereof in a direction of the axis of the crankshaft, a distal-side wall portion that is in sliding contact with an end face of the inner rotor on the distal side and has, on a proximal side thereof in the direction of the axis of the crankshaft, a proximal-side wall portion that is in sliding contact with end faces of the inter rotor and the intermediate member on the proximal side, the crankshaft is provided with a restriction wall that is in sliding contact with an end face of the intermediate member on the distal side, an oil seal designed to seal a space between the distal-side wall portion and any one of the crankshaft and a member coupled integrally to the crankshaft is provided, the first fitting hole penetrates the intermediate member in the direction of the axis of the crankshaft, and the second fitting hole penetrates the inner rotor in the direction of the axis of the crankshaft.
 6. The oil pump according to claim 1, further comprising a crank pulley that includes: a circular pulley body portion; and a pulley cylindrical portion which is provided at a center of the pulley body portion and in which the one end of the crankshaft is inserted unrotatably, wherein the first fitting portion is formed in an outer circumferential face of the pulley cylindrical portion.
 7. The oil pump according to claim 1, wherein the internal combustion engine body has: a cylinder block; and a chain cover that is coupled to an end face of the cylinder block on one end side thereof in the direction of the axis of the crankshaft, and forms a space with the cylinder block therebetween, and the pump housing is provided in the chain cover.
 8. The oil pump according to claim 1, wherein the inner rotor has a cylindrical boss portion having an axis of the inner rotor as a center thereof, and the pump housing has a circular fitting hole in which the boss portion is fitted rotatably.
 9. An oil pump for an internal combustion engine, comprising: a pump housing coupled to an engine body of the internal combustion engine; a crankshaft supported on the engine body to be rotatable about a crankshaft rotational axis, the crankshaft having a protruding end protruding from the engine body; a first fitting portion coupled to the protruding end of the crankshaft; an intermediate member slidably coupled to the first fitting portion, the intermediate member comprising: a first hole wall surrounding the crankshaft rotational axis and defining a first fitting hole in which the first fitting portion is provided, the first hole wall slidably supporting the first fitting portion in a first direction orthogonal to the crankshaft rotational axis so that the intermediate member rotates together with the crankshaft; and a second fitting portion provided to be opposite to and around the first hole wall; an inner rotor slidably coupled to the intermediate member to be rotatable about an inner rotor rotational axis parallel to the crankshaft rotational axis, the inner rotor comprising: a second hole wall surrounding the inner rotor rotational axis and defining a second fitting hole in which the second fitting portion is provided, the second hole wall slidably supporting the second fitting portion in a second direction orthogonal to the first direction and the crankshaft rotational axis so that the inner rotor rotates together with the intermediate member, one of the first direction and the second direction being in parallel with a line segment joining the crankshaft rotational axis and an axis of a crankpin of the internal combustion engine which is closest to the protruding end of the crankshaft; and an inner rotor outer circumferential part provided to be opposite to and around the second hole wall; and an outer rotor accommodated in the pump housing to be rotatable about an outer rotor rotational axis parallel to the crankshaft rotational axis and comprising an outer rotor inner circumferential part surrounding the outer rotor rotational axis to mesh with the inner rotor outer circumferential part.
 10. The oil pump according to claim 9, wherein the first fitting portion, the first fitting hole, the second fitting portion, and the second fitting hole are arranged on one plane orthogonal to the crankshaft rotational axis.
 11. The oil pump according to claim 9, wherein the first fitting portion has: a pair of first side faces that extend parallel with the first direction with the axis of the crankshaft interposed therebetween; and a pair of arcuate first side end faces that join opposed end parts of the pair of first side faces, the first hole wall has: a pair of planar first hole wall faces that are in sliding contact with the paired first side faces respectively; and a pair of arcuate first hole wall end faces that join opposed end parts of the pair of first hole wall faces, and each first hole wall end face has a curvature smaller than each first side end face.
 12. The oil pump according to claim 9, wherein the second fitting portion has: a pair of second side faces that extend parallel with the second direction with the axis of the crankshaft interposed therebetween; and a pair of arcuate second side end faces that join opposed end parts of the pair of second side faces, the second fitting wall has: a pair of planar second hole wall faces that are in sliding contact with the paired second side faces respectively; and a pair of arcuate second hole wall end faces that join opposed end parts of the pair of second hole wall faces, and each second hole wall end face has a curvature smaller than each second side end face.
 13. The oil pump according to claim 9, wherein the protruding end of the crankshaft penetrates the pump housing, the pump housing has, on a distal side thereof in a direction of the crankshaft rotational axis, a distal-side wall portion that is in sliding contact with an end face of the inner rotor on the distal side and has, on a proximal side thereof in the direction of the crankshaft rotational axis, a proximal-side wall portion that is in sliding contact with end faces of the inter rotor and the intermediate member on the proximal side, the crankshaft is provided with a restriction wall that is in sliding contact with an end face of the intermediate member on the distal side, an oil seal designed to seal a space between the distal-side wall portion and any one of the crankshaft and a member coupled integrally to the crankshaft is provided, the first fitting hole penetrates the intermediate member in the direction of the crankshaft rotational axis, and the second fitting hole penetrates the inner rotor in the direction of the crankshaft rotational axis.
 14. The oil pump according to claim 9, further comprising a crank pulley that includes: a circular pulley body portion; and a pulley cylindrical portion which is provided at a center of the pulley body portion and in which the protruding end of the crankshaft is inserted unrotatably, wherein the first fitting portion is formed in an outer circumferential face of the pulley cylindrical portion.
 15. The oil pump according to claim 9, wherein the engine body has: a cylinder block; and a chain cover that is coupled to an end face of the cylinder block on one end side thereof in the direction of the crankshaft rotational axis, and forms a space with the cylinder block therebetween, and the pump housing is provided in the chain cover.
 16. The oil pump according to claim 9, wherein the inner rotor has a cylindrical boss portion a center of which is the inner rotor rotational axis, and the pump housing has a circular fitting hole in which the boss portion is fitted rotatably. 